Swimming bacteria: from individual swimmers to dense suspensions

B. subtilis is often used to investigate collective swimming behaviour in concentrated bacterial suspensions despite the fact that little is known about swimming of individual cells. It is assumed to be similar to the paradigm peritrichous microorganism E. coli which generates thrust with a single propulsive flagella bundle. Using live cell flagella imaging, we directly visualise and compare the swimming mechanism between these two species. We also present direct visualisation of flagella filaments during reversal events which have been highlighted as a possible mechanism to facilitate collective swimming amongst larger number of interacting cells. And imaging of flagella filaments in the setting of collective swimming behaviour reveals how the run and tumble behaviour of cells varies as a function of concentration.